While many products are transported in packages or containers, many other products are transported in bulk where the desired amount of product is placed into the vehicle that is to be used to transport the product. The vehicles typically used to transport bulk products include trucks, trailers, rail cars, carts, wagons, and other various containers with open tops. These vehicles typically include an open top to facilitate placing the bulk product into the vehicle.
To reduce the potential of product falling out of the vehicle as the vehicle is moved and to reduce the potential of the product being damaged by environmental factors, it is customary to place a cover over the open top of the vehicle. To facilitate placing the bulk product into the vehicle, the cover is typically retractable such as rolling up.
An example of one such cover is marketed under the designation SRT-2 by AgriCover such as is illustrated in FIG. 1. This tarp system uses the tarp to pull the roll tube across the hopper as it rolls up the tarp. An internal torsion spring in each spool (similar to a garage door spring) is preloaded to provide tarp tension in the closed position. As the tarp is being rolled up and begins to grow in diameter, the roll tube begins moving faster than the cable is unrolling and the spools begin to turn slightly on the roll tube, winding the spring even tighter.
This increase in speed occurs because the tarp diameter becomes larger than the spools and the roll tube moves farther per revolution than the spools whose circumference remains the same. To close the tarp, the motor reverses and the torque tensioned spools “reel in” the cable, pulling the tube back across the hopper.
Other side roll-up tarp systems are marketed by Michel (FIG. 2) and Shur-Co., the assignee of this patent application, under the designation Super Duty Swing Arm Electric System (FIGS. 3-4). Both of these tarp systems use extension springs and spools that are rigidly mounted to the roll tube.
Michel's tarp system uses a tapered grooved spool and Shur-Co uses a narrow, flat bottom, grooveless cable spool. Both systems pull cable from a side mounted tube at a 90° angle as the roll tube moves across the caps. Both systems unroll cable from their respective spools as the tarp is opened. Both systems' roll tubes move further than the amount of cable unrolled, which results in extending the springs as the tarp moves to the open position thus giving the force needed to keep the cable tight allowing the spools to reel in the cable which closes the tarp.